D-O Warming Episodes During the Last Glacial Period From the ReCAP Ice Core

Understanding the physical processes that drive the Earth's climate system throughout a Dansgaard-Oeschger (D-O) event remains an important open scientific question in paleoclimate research. The spatial pattern of D-O warming holds clues to the origin of D-O events. Here we follow previous studies using the 15N/14N of N2 (d15N) to identify thermal fractionation signatures associated with the abrupt warming episodes (Kindler et al. 2014) recorded in the ReCAP ice core from E. Greenland. All totaled, we measured 339 discrete samples for d15N with a pooled error of 5.7 permeg. We then employed a firn densification algorithm (Buizert et al. 2012) to estimate the magnitude of the warmings. The work flow involved using the PSU d15N data along with d18Oice data from our Danish colleagues and a densification models to generate records of paleo temperature at ReCAP (Buizert et al. 2018). The magnitude of the temperature shifts at the onset of the interstadial events are ~40% lower than those recorded at NGRIP.

The smaller temperature jumps recorded at ReCAP are somewhat unexpected given the proximity of ReCAP to the GIN seas where North Atlantic Deep Water (NADW) is formed. We have begun to investigate GCM modeling studies that include both an ocean and an atmosphere tuned to the last glacial period that mimic D-O events. One such study (Guo et al. 2018) illustrates a strong E-W temperature gradient over Greenland during simulated stadial/interstadial transitions. It is interesting to note that simulated perennial sea ice on the E. Greenland coast appears to persist down to ~66^oN latitude throughout the simulated interstadial period. This is well south of ReCAP (71^oN) implying that sea ice effectively insulated ReCAP from the thermohaline circulation changes explaining the relatively muted magnitude of abrupt events in that core.